1. Field of the Invention
This invention relates to synchronizing a receiver to a transmitter by use of a phase locked loop (PLL) and more particularly to such synchronization which is accomplished by using a portion of the data bit stream for the synchronization pulses.
2. Description of the Prior Art
The use of optical fiber in the telecommunications industry has grown. One proposed use is in a system to provide service to a multiplicity of subscribers. The use of optical fiber in such systems is attractive as the fiber has a wide bandwidth which allows both traditional telecommunication services (voice and data) and video service to be provided to the subscriber. The traditional telecommunication services can be provided in such a system by using a digital transmission scheme.
In a system designed to provide such service over optical fiber to subscribers, it has been decided to use the 850 nm wavelength so that relatively inexpensive light emitting diodes (LEDs) can be used instead of lasers. As in all such systems, it is necessary that both ends of the system be synchronized with each other at all times. It is desirable that such synchronization be accomplished in a relatively easy and simple manner. It is also desirable that PLLs be used in achieving synchronization. It is further desirable that during the time synchronization is being achieved, the system minimize the on time of the LED. This minimizes LED power consumption.
The synchronization scheme described herein meets those requirements. Inherent to such a scheme is that LED on time and power consumption are also both minimized after synchronization has been achieved during those intervals when nothing is being transmitted to the subscribers.